Cabot's "Princess Diaries Volume X: Forever Princess" was published in 2009. ©HarperCollins

Cabot’s “Princess Diaries Volume X: Forever Princess” was published in 2009.

(Relaxnews) – Meg Cabot is returning as author of “The Princess Diaries” in 2015, but this time will focus on Mia Thermopolis’s life as an adult.

Just like her fans, Mia has grown up, and “Royal Wedding” sees her prepare for marriage to long-term beau Michael.

At the same time, it emerges that Mia has a half-sister, Olivia Grace, who, just like Mia in the original novels, must now come to terms with being an ordinary girl and part of a royal family.

As such, Olivia is to receive her own spin-off series starting with “From the Notebooks of a Middle School Princess.”

And Mia’s own escalating adventure involves her proving her own suitability to rule Genovia as her father is forced out.

“Royal Wedding” will be the 11th Princess Diaries book, and its 2015 publication date coincides with the 15th anniversary of the series as a whole, wrote Meg on her website.

Meanwhile, “From the Notebooks…” will be the first time Cabot will have written and illustrated the same book, with the author noting that Olivia Grace’s biracial background holds “a special resonance for me and my family,” a reference to her own adoptive brother.

“I’ve been planning this book for some time. I got the inspiration a few years ago from actual goings-on in a certain royal family of a small European principality,” she confessed, while reminding fans of Disney’s two “Princess Diaries” movies that Prince Philippe may have died in the adaptations but remains very much alive in the books.